During the operation of printing presses, the blankets on the blanket cylinders and the plates on the plate cylinders accumulate foreign matter, such as dried ink or ink build-up, paper, lint, clay, dirt and the like that must be removed to maintain high quality printing. As a result thereof, during a specific run or printing job, the blankets and plates must be cleaned at various times. The blankets must also be cleaned to remove the image when a particular printing job is completed.
To be effective, the blanket and plate cleaning devices must be capable of removing the foreign matter from the surface being cleaned and then discharging such removed materials from the cleaning device. For this purpose, as shown in U.S. Pat. No. 4,015,307 assigned to the same assignee as the present application, blanket cleaning devices are known which include a cylindrical brush roller that is engageable with the blanket cylinder and rotatable against the blanket or plate cylinder. Solvents preferably are applied to the brush roller during the scrubbing cycle to enhance the cleaning action, and a flicker bar is mounted in engaging relation with the underside of the brush roller for causing the bristles of the brush to flex as they are directed over the flicker bar and eject foreign matter and solvent carried by the brush roller from the blanket cylinder.
While such cleaning devices have been found to effectively clean blanket cylinders, they have had certain design and operating limitations. Since the brush roller rotates against the blanket cylinder and the flicker bar engages the underside of the brush roller, reactionary forces exerted on the brush roller by the resistance of the flicker bar increase the pressure by which the brush roller bears against the blanket cylinder. When the brush roller strikes a gap in the blanket cylinder between blankets, the brush roller tends to be suddenly urged forwardly and then bounce rearwardly in reaction thereto. As the speed of the brush roller increases, so does the bouncing and vibratory action of the brush roller, which can result in undesirable streaking on the blanket being cleaned. The speed of brush roller rotation, therefore, must be limited to prevent such streaking. Moreover, since rotation of the brush roller is resisted both by its engagement with the blanket cylinder, as well as the flicker bar, a relatively high torque drive motor generally is required for the brush roller. The action of the flicker bar on the brush roller, furthermore, has been found to remove approximately 10 to 25 percent of the solvent that is applied to the brush roller during the cleaning operation. Hence, the cleaning device must be provided with solvent in sufficiently large quantities to compensate for the amount of solvent that is removed by the flicker bar, which increases the operating costs of the system.
It also is necessary that blanket and plate cleaning devices not allow excessive amounts of solvent to be applied to the moving sheet material. Since dryers utilized in high quality printing lines can accommodate only predetermined levels of solvent without creating a potentially flammable condition, caution must be taken to ensure that solvent applied to the blankets and plates during a cleaning operation and in turn to the sheet material for transport through the dryer does not exceed the capacity of the dryer. Indeed, while it is often desirable to employ four to ten printing units operating on a moving web, depending upon the color and printing requirements, the number of printing units may be limited by the amount of solvent that is imparted to the web from the blanket and plate cleaning devices. Hence, the capacity of the dryer, together with the amount of solvent applied to the web by the blanket or plate cleaning devices, can limit the printing units that may be available for the printing operation. Since heretofore it has been difficult to precisely control the amount of solvent applied to the web, it has been equally difficult to reliably determine the maximum number of printing units that may be employed without exceeding the safety limits of the dryer.
The blanket and plate cleaning devices, furthermore, must permit reliable discharge of solvent and foreign matter removed from the brush roller without creating a clogged or overflow condition that can cause the brush roller to apply excessive solvent to the moving web. In addition, in prior blanket and plate cleaning devices dangerous conditions can result in the event of a breakdown or malfunction in the mechanical or control systems of the cleaning device. For example, when solenoid control valves are employed, if the blanket or plate cleaning device breaks down with the valve in an open condition, solvent may be continuously directed onto the brush roller during the period of the malfunction, again resulting in the application of excessive solvent to the web or sheet material which is carried to the dryer. Moreover, in prior blanket and plate cleaning devices, it is frequently difficult to effect service or repair, and space limitations about the press often necessitate the added cost of custom design and installation.
Large newspaper printing presses have further distinct blanket cylinder cleaning requirements. A complete newspaper must be simultaneously printed on the printing press line within strict time restraints, and the need therefor has existed for maintaining the printing cylinders in a clean condition without interruption of the printing operation. Heretofore, this has created significant problems. Due to the ineffectiveness of conventional blanket cleaning devices on such newspaper printing lines the build up of contaminants on the blanket cylinders can occur to the extent that the web tends to adhere to the blanket cylinders, causing the web to ultimately be damaged or torn, which in turn interrupts the entire printing operation and results in costly down time and the waste of large amounts of paper. Large metropolitan newspapers can incur an excess of $50 million a year in waste paper alone associated with inadequately cleaned blanket cylinders.
Such large newspaper printing presses furthermore are relatively complex, comprising a number of printing towers each typically having a plurality of individually configured vertical stacks of printing units. Conventional blanket cleaning devices have not been well suited for adaptation in such printing lines without considerable custom design and engineering. A further problem with such large newspaper printing lines, particularly in metropolitan areas, is the limitation in the amount of volatile organic compounds or solvents that can be used in the printing and cleaning operations. The need for monitoring and precisely controlling the use of such volatile organic compounds has existed in order to ensure a safe environment and to maintain compliance with regulatory requirements. Again conventional blanket cleaning systems have been inadequate in that regard.